paid. "Collusion" requires secret, concerted efforts. If you'd get paid $5,000 to help someone buy one home and $50 to help someone buy another home, and they are decently comparable homes in meeting your clients' needs, which home would you be more interested in showing? It's not like the NAR or any local association of realtors is secretly meeting to tell all agents "don't show your buyers this home and it's being listed by a discount broker." That would be collusion.
Otherwise, your point is correct that (good) agents will help their clients buy the best home for them (the clients) regardless of the amount of commission they (the agents) receive.